93 F-150 ENGINE STALLS - KOER CODE 311

1993 All Other Makes

My f-150 has 150000 miles and recently started stalling when first started it acts flooded untill I rev it up hard then comes out of it. Some days it will stall at every stop then run fine for up to a week. I ran the codes and 311 air system not functioning came up.
the air pump was noisy so I replaced it. The problem hasen't changed and the code is still there. Could it be the air bypass valve and would this cause the stalling?

Thanks for the reply. Just wondering if you ever resolved the code? I'm beginning to believe the emission system is a boat anchor after a few years and does not contribute to performance with the exception of smog emission.